In the field of aquaculture, it is usual to treat the bodies of water containing the cultured or bred species with various treatment agents to improve the quality of the water. It is also usual to treat the bodies of water to indirectly treat the living organisms cultured or bred inside the bodies of water, for example to fight various diseases or parasites. For instance, it is known to control parasites such as Gyrodactilus sp., Ichthyobodo sp. (or Costia sp.) or salmon lice (Lepeophtheirus salmonis) in the breeding of fish by treating a body of water containing the fish with an active chemical compound such as hydrogen peroxide, sodium percarbonate, organo phosphates, pyrethroids or peracetic acid.
As disclosed in U.S. Pat. No. 5,355,838, a method for preventing fish-borne parasites from spreading to another area of water without such parasites comprises forcing all fish which are going to pass into this other area of water through a bath of water containing an active substance which kills or removes the fish-borne parasites without killing or seriously injuring the fish.
Another example is disclosed in U.S. Pat. No. 5,313,911 wherein a method for controlling parasites in fish breeding comprises screening off the water containing fish and parasites so that the exchange with the surrounding water is essentially stopped and supplying the water in which fish are maintained with an amount of hydrogen peroxide from 1.2 to 2.9 g/l during a definite period of time. According to U.S. Pat. No. 5,313,911, it has proved essential that the concentration gradients of the hydrogen peroxide in the water be minimized. It is thus advisable to add the hydrogen peroxide in the form of an aqueous solution having a concentration from 10 to 70% through a pipe or a hose having a plurality of nozzles disposed below the water surface.
However, this process has the disadvantage that the fish which are located close to the nozzles are still in contact with a very high concentration of hydrogen peroxide while the fish which are located far from the nozzles will probably not be in contact with an effective amount of hydrogen peroxide during the recommended period. And if the process is conducted using very low concentrations of hydrogen peroxide, other drawbacks will arise such as the necessity to move big amounts of dilute solution on the treatment site or the necessity to pre-dilute the hydrogen peroxide solution in a dosing chamber. Furthermore, using a very dilute hydrogen peroxide solution means to add a huge amount of said solution to the body of water, which is usually a substantially enclosed water system and has therefore a finite volume.